1. Field of the Invention
The invention relates to a modem for selectively connecting a computer to a land line or to a cellular telephone. More specifically, the invention relates to a modem that has circuitry for selecting between two communications jacks, the first of which connects to an external DAA or to a cellular telephone, and the second of which connects to a land line via a DAA internal to the modem.
2. Description of the Related Art
In the year 1948, a simple device was invented that was to have a profound impact on modern life. That device was the electronic transistor. It was the transistor that first made computers technically practical. These first computers were behemoths--centralized machines servicing a large number of users and a large number of tasks. While the economic impact of these mainframe systems was tremendous, it was not until the subsequent development of the microprocessor, and the attendant development of the personal computer, that computer technology directly impacted the lives of the modern consumer and small businessman.
When the personal computer market exploded in the 1980's, it filled needs very different from those filled by the mainframe computer. Personal computers were used to perform individual, isolated tasks without communication with other computers except perhaps through manual exchange of floppy disks. The mainframe computer still served the requirements of centralized data access and coordination among a large number of users.
But as the personal computer market developed, the advantages and possibilities of communicating among these machines became apparent. One of the methods of communication that rose to the forefront was modem technology. By connecting modems to their personal computers, users could directly transfer data between and communicate in realtime with mainframes and other personal computers. For example, bulletin board systems have now become very popular, allowing a large number of users to remotely upload and download free software, exchange information, and engage in online forums. With modems'rising speeds, increased standardization, and expanding uses, one is now hard pressed to find a personal computer system that does not use a modem.
While intercommunication between personal computers and mainframes was on the rise, another development was to have an impact on the need for communicating with distant systems. Personal computers were becoming smaller. From the original large under-the-desk machines, desktop machines evolved, then transportables, and finally laptop and notebook computers. These laptops and notebooks are typically very mobile, easily traveling from city to city, state to state, and even country to country. But the advantage of portability itself presents a problem: while stationary machines can be conveniently connected to communication networks via a telephone line, laptop users might wish to establish communication links from countries with which their laptop's modems are not compatible, or they might wish to communicate where normal phone connections are not available, such as from a car, bus, or train.
Although standardized within a single country, telephone systems around the world are generally non-standard, and different hardware is required to connect to these various systems. Thus, a modem configured to connect to one country's phone system would generally not be suitable for connection to another's. The physical connection to a particular national phone system is made through what is known is a data access arrangement, or DAA. Each particular phone system will have its own associated DAA. Typically, modems are constructed with a DAA built in. That, however, means that a modem suitable for one country would not be able to connect to another country's phone system, or would at least require an external adaptor that would typically require external power.
With portable, laptop, and notebook computers, the problem of the different DAA's required for each country becomes even more apparent. One would not wish to buy a notebook or laptop with a built-in modem that could not be easily modified for use in another country. An international traveler might never be sure to which country's phone system he would primarily wish to connect. For example, if he lived in the United States, he would want his laptop's modem to be suitable for directly connecting to the United States'phone system. But if he moved to Germany, he would wish his laptop's modem to be suitable for directly connecting to the German phone system. But further, if our hypothetical businessman, living in the United States, traveled to Germany, he would want to be able to connect his laptop into the German phone system even though his laptop's modem is internally configured for connection to the United States phone system. This problem has been resolved to some extent by the use of external DAA units.
For a computer user in a car, bus, or train, another recent technological development provides possibilities for laptop and notebook modem communications. With the recent expansion of cellular telephone systems, cellular telephone has become a very common, and very portable, item. Not surprisingly, crude attempts at a marriage between cellular telephone technology and modem technology have keen made using laptop and notebook computers and cellular phones. By connecting a laptop to a cellular phone, one can access a telephone network in generally the same way as by directly hooking to a telephone wall outlet, or via a "land line."
It would be desirable to make as seamless of a link between a computer system and cellular telephone systems or various countries'phone systems. That is, it would be desirable to be able to transparently use different countries' phone systems depending on which the computer was then connected to, or to instead transparently use a cellular telephone.